Optionally shave time off the armv4_5 run_algorithm() code:  let
them terminate using software breakpoints, avoiding roundtrips
to manage hardware ones.

Enable this by using BKPT to terminate execution instead of "branch
to here" loops.  Then pass zero as the exit address, except when
running on an ARMv4 core.  ARM7TDMI, ARM9TDMI, and derived cores
now set a flag saying they're ARMv4.

Use that mechanism in arm_nandwrite(), for about 3% speedup on a
DaVinci ARM926 core; not huge, but it helps.  Some other algorithms
could use this too (mostly flavors of flash operation).

git-svn-id: svn://svn.berlios.de/openocd/trunk@2680 b42882b7-edfa-0310-969c-e2dbd0fdcd60